The present invention relates generally to containers, and more particularly, to containers prepared from heat-sealable laminate structures that include a layer of foamed polymer. The heat-sealable laminate structures of the present invention may include barriers commonly used to prevent oxygen from being transmitted to the product and/or to prevent water loss from the product.
Paperboard, heat-sealable polyethylenes, aluminum foil, and/or barrier polymers such as an ethylene vinyl alcohol co-polymer (EVOH) are primary components of many known containers.
Heat-sealable polyethylenes are commonly used as the product-contact layer of many known containers to provide a water/water vapor barrier to the structure, but they may have a deleterious effect on some products such as citrus juices by absorbing product flavor components and/or aroma oils. In addition to eroding product quality, the absorption of these oils may cause decay of the heat seals of containers by stress-cracking the polyethylene to the extent that the liquid may penetrate the paperboard.
Container structures that use paperboard may have a number of shortcomings, including: deterioration of the paperboard if saturated by liquid; a low strength to weight ratio; and difficulty in folding or creasing. In some cases, paperboard does not collapse or compress to a smaller caliper as desired during conventional heat sealing. The paperboard may contain contaminating aromas, and it may contain microorganisms, either of which may require some form of raw edge protection to prevent product contamination. During heat sealing, the heat may cause water to be vaporized from the paperboard, resulting in de-lamination of polyethylene coatings.
For at least these reasons, a need exists to replace the paperboard in existing container structures with a material that: is impervious to liquids such as water and oils; has greater strength, flexibility, and durability at a lower cost and weight; is non-scalping with regard to aromas, flavors, and vitamins; may provide a better seal by flowing and compressing during heat sealing; may permanently retain creases uniformly with direction; may be formed into cartons of various shapes; and that eliminates the need for raw edge protection to prevent product contamination.
The present invention provides containers prepared from heat-sealable laminate structures, either with or without a barrier that include a layer of foamed polymer that satisfy some or all of these needs. Also, the foamed polymer layer of the present invention provides benefits such as the ability to specifically engineer it for caliper, density, cell size, and skin surface along with the opportunity to process the material either in the direction of the web or across the web without reducing the inherent strength of the material. For example, the foamed polymer layer may be compressed and/or collapsed to a smaller caliper in the seal area during heat sealing. In addition, the foamed polymer layer may be creased to a smaller caliper that may allow for shorter radius bends that cause less stress on the other layers of the laminate structure.
In preferred embodiments of the present invention, the layer of foamed polymer is impervious to liquids, and it is more flexible, durable, and resilient than paperboard. Additionally, the layer of foamed polymer may be easier to fold and crease than paperboard while offering improved compressibility. The strength to weight ratio of foamed polymers is also preferably greater than paperboard and, as a result, the present invention may allow the production of containers at a lower cost than paperboard containers that serve the same function.
When combined with a barrier layer in addition to the foamed polymer layer, the heat-sealable laminate structures of preferred embodiments provide oxygen barrier properties.
Finally, certain of the preferred embodiments offer the additional benefits of microwave heating and/or non-absorption of essential oils, flavors, or vitamins.